Dry etching, as that term is used in the semiconductor industry, encompasses a number of related processes. The common feature of these processes is the presence of a gas or plasma which contains at least one reactive specie and which is energized by the application of RF energy. The gas or plasma is placed in contact with the structure being etched, a reaction takes place at the surface of the material and reacted material is removed in gaseous form.
The various distinct dry etching processes include reactive ion etching (RIE) and plasma etching. While the precise definition of these terms is not completely settled, the different processes are typically characterized by the pressure of the gas or plasma, the frequency of the RF energy supplied thereto, the configuration of the chamber in which the reaction takes place, the method of applying the RF energy to the gas or plasma and the chemistry of the gas or plasma. The generic term dry etching will be used throughout to refer to all of these related processes.
A structure which is of increasing interest in the field of integrated circuit manufacturing comprises a two layer "sandwich" of polysilicon underlying a refractory metal silicide. Such a structure typically overlies a thin layer of silicon dioxide dielectric, for example, and comprises the gate of an insulated-gate field effect transistor (IGFET) device. It has been found that such a structure is quite difficult to etch using dry etching techniques because of the differences in the response of the silicide and polysilicon materials to the etching processes.
For small geometry devices, it is necessary to carefully control the edge profile of the structure being etched. In addition, since the underlying dielectric is often quite thin, a process with a very high selectivity to silicon dioxide is required. Despite numerous attempts, the prior art does not disclose a dry etching process which can effectively etch a silicide/polysilicon structure with good edge profile control and high selectivity to an underlying dielectric.